EFFECT OF SEED PRIMING ON INFECTION WITH WHITE TIP NEMATODE (Aphelenchoides besseyi), SEED-BORNE FUNGI, RICE YIELD, AND YIELD COMPONENTS IN EGYPT.

Abstract

Rice is the second staple food crop after wheat in Egypt. White tip disease of rice leaves induced by the rice leaf nematode, Aphelenchoides besseyi (Christie, 1942), is widespread nearly in all rice ecosystems all over the world, causing remarkable yield reduction to susceptible cultivars. The losses reach to 47% in Egyptian rice Reiho cultivar. Rice seeds are known as the main source of the disease. The present study was conducted to evaluate the effect of seed priming on white tip nematode infection in rice and seed-borne fungi at different plant growth stages. Severely-infected Reiho rice seeds were primed for 48 hr in solutions of NaCl, CaCl2, Na2CO3, MgSO4, CuSO4 and micronized sulfur, separately or in mixtures of two salts except for the sulfur treatment. The primed seeds and the corresponding control non-primed counterparts were then rinsed for three times using tap water and incubated at 30oC to asses the germination percentage, which ranged between 96 to 100% with no significant difference between the primed and non-primed seed treatments. In the lab testing, the maximum seedling vigor index and root / shoot ratio were obtained using seedlings raised from seeds primed with 5 g/L solutions of sulfur (80%WP) followed by sulfur + CaCl2, NaCl and CuSO4. At nursery level, root/shoot ratio increased with all primed seed treatments except with those treated with NaCl solution. Two field experiments were conducted during the 2007and 2008 rice growing seasons. All seed priming treatments significantly enhanced most of the agronomic traits and increased yield in comparison with the non-primed infected or healthy seeds. Soaking in sulfur solution at the concentration of 5g/L and its combinations with the other salts at half dose of each gave the highest mortality of white tip nematode, lowest percentage of white tip infection, and least disease severity. Sulfur and NaCl is then proved to be the most effective priming mixture that can reduce white tip nematode infection. For seed-borne fungi, the treatment with CaCl2 alone or in its all combinations has positive effects in elimination of the Fusarium Moniliforme, Helminthosporium oryzae and Alternaria padwickii in comparison with the water treatment control. CaCl2 completely eradiated F. moniliforme. Seed treatment with mixtures of salts reduced the fungal growth more than did one salt alone. Generally, all seeds primed with salts showed lower levels of infection with F. moniliforme comparing with the control. The treatment with CuSO4 solution at 1.5g/L gave complete protection from seed-borne fungi